[Bug tree-optimization/29751] New: Missed optimization of restrict pointer assigned value

[Bug tree-optimization/29751] New: Missed optimization of restrict pointer assigned value

[burnus at gcc dot gnu dot org]

In the following program, the if() is only removed if one removes the line
"r[1]=0;". (4.3.0 20061107; x86_64-unknown-linux-gnu-gcc)

#include <stdlib.h>
void foo (void);
int main() {
  int *restrict r;
  r = malloc(2*sizeof(int));
  r[0] = 0;
  r[1] = 0;
  if(r[0]) foo();
  return 0;
}


main ()
{
  int * restrict r;
  void * D.1998;
<bb 2>:
  D.1998 = malloc (8);
  r = (int * restrict) D.1998;
  *r = 0;
  *(r + 4B) = 0;
  if (*r != 0) goto <L0>; else goto <L1>;
<L0>:;
  foo ();
<L1>:;
  return 0;
}


-- 
           Summary: Missed optimization of restrict pointer assigned value
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-11-14 01:06 -------
This is a problem of our VOPs not having base+offset and has nothing to do with
restrict.


int f(int *r)
{
  r[0] = 0;
  r[1] = 0;
  if(r[0]) foo();
}

is enough to reproduce the issue.  Also I think there might be a couple dups of
this with respect of structs instead.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Missed optimization of      |not optimizing access a[0] ,
                   |restrict pointer assigned   |a[1]
                   |value                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-06-11 00:30 -------
Confirmed, this is only a tree level missed optimization.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |alias, TREE
   Last reconfirmed|0000-00-00 00:00:00         |2007-06-11 00:30:03
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-03-14 21:21 -------
Related to PR34172, but not fixed.  MEM_REF will get this right as we
effectively
have array refs on pointers there.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-06-11 00:30:03         |2008-03-14 21:21:32
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2008-04-07 01:28 -------
Hmm, if we change r to be an array, fre does the correct thing but shouldn't it
do the correct thing for the non array case too?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2008-04-07 08:51 -------
Only if you extend refs_may_alias_p, as for pointers you have

 p_2 = p_1 + 1;
 *p_2
 *p_1

and it doesn't follow def-use chains to see the pointer-plus to disambiguate
both pointer de-references.  With arrays you see

 a[0]
 a[1]

which it handles fine.  It also should handle

 (*p_2)[0]
 (*p_2)[1]

fine (if you convert p_! to (int *)[] first).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2009-06-09 02:35 -------
I have a simple patch (which needs some cleanups but it works).


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|rguenth at gcc dot gnu dot  |pinskia at gcc dot gnu dot
                   |org                         |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2009-08-05 17:52 -------
Created an attachment (id=18307)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18307&action=view)
Patch which I am testing

This patch fixes the problem including a+1 and a+2 not aliasing each other.
It adds two testcases and removes a xfail on one.
It also fixes a bug in cfgexpand.c (update_alias_info_with_stack_vars) so that
it does not create SSA_NAMES with a define statement of NULL.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
      Known to work|                            |4.6.0
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0

--- Comment #11 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-25 10:30:28 UTC ---
The original testcase is fixed during early FRE since we have MEM_REF, and
DCE makes main empty even in 4.7.

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-25 09:14:07 UTC ---
(In reply to comment #9)
> Created attachment 25847 [details]
> more correct patch
> 
> An updated patch which is more correct than the previous patch and it works
> correctly with MEM_REF which has an offset.  Also moves some code to do
> addition of the bit offset to a function.
I just noticed it does not have the fix for
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44838 in it really.

Will retest and submit tomorrow.

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #18307|0                           |1
        is obsolete|                            |

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-11-17 22:03:34 UTC ---
Created attachment 25847
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25847
more correct patch

An updated patch which is more correct than the previous patch and it works
correctly with MEM_REF which has an offset.  Also moves some code to do
addition of the bit offset to a function.

[Bug tree-optimization/29751] not optimizing access a[0] , a[1]

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29751

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-09-23 22:09:14 UTC ---
(In reply to comment #7)
> Created attachment 18307 [details]
> Patch which I am testing

There is one bug in that patch which I have a fix for.